hv: a few fixes for multiboot2 boot

- need to specify the load_addr in the multiboot2 address tag. GRUB needs
  it to correctly calculate the ACRN binary's load size if load_end_addr is
  a non-zero value.

- multiboot2 can be enabled if hypervisor relocation is disabled.

- print the name of the boot loader. This might be helpful if the boot
  loader, e.g. GRUB, inludes its version in the name string.

Tracked-On: #4441
Signed-off-by: Victor Sun <victor.sun@intel.com>
Signed-off-by: Zide Chen <zide.chen@intel.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>

hypervisor/boot/guest/vboot_wrapper.c

@@ -42,6 +42,7 @@ void init_vboot(void)
 		{"PXELINUX", DIRECT_BOOT_MODE},
 	};
 
+	printf("Detect bootloader: %s\n", mbi->mi_loader_name);
 	for (i = 0U; i < BOOTLOADER_NUM; i++) {
 		if (strncmp(mbi->mi_loader_name, vboot_bootloader_maps[i].bootloader_name,
 			strnlen_s(vboot_bootloader_maps[i].bootloader_name, BOOTLOADER_NAME_SIZE)) == 0) {

hypervisor/boot/multiboot.c

@@ -68,6 +68,10 @@ int32_t sanitize_multiboot_info(void)
 		ret = -EINVAL;
 	}
 
+	if (acrn_mbi.mi_loader_name[0] == '\0') {
+		pr_err("no bootloader name found!");
+		ret = -EINVAL;
+	}
 	return ret;
 }